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This paper aims to provide a precise transformation model for the geoid heights between earth geopotential models and regional vertical datum in geodetic applications. With this purpose, Earth Gravitational Model 2008 (EGM08), which is ultra-high-resolution geopotential model, that is complete spherical harmonic degree and order 2190 is considered and fitted to the local vertical datum in three local test areas in west and south of Turkey. The observations at GPS/leveling benchmarks were used for fitting the EGM08 to the local height reference surface and a couple of mathematical methods were evaluated, namely similarity transformation model (STM), polynomial regression model (PRM), least squares collocation (LSC), spline interpolation model (SIM). They are commonly used for corrector surface fitting approaches in height datum studies. Their performances were assessed depending on the statistics at test benchmarks. The results show that fitting of the differences between the GPS/leveling, EGM08-derived geoid heights with LSC, and SIM supplies more accurate solutions than STM and PRM. The accuracies of the achieved models (improved from EGM08 global model) are tested in the several GPS/leveling benchmarks throughout Turkey; the external model accuracy has been estimated as ±4-5 cm. In this aspect, this study will provide benefits as both representing the performance of EGM08 model in given local areas and clarifying the modeling performances of the applied transformation approaches for fitting of EGM08 geoid models to GPS/leveling defined vertical datum. [ABSTRACT FROM AUTHOR]

Abstract: Both seismological and geodynamic studies emphasize that the Aegean region is deforming internally mainly under pure shear stress and rotating in an anti-clockwise direction relative to the Eurasia plate. The Aegean region is seismically the most active region in western Anatolia, which comprises the Hellenic Arc, Greece, and western Turkey. Izmir is the third largest city in Turkey, with a population about 2.7 million in 2010. The Tuzla fault has a particular importance in terms of its proximity to the city of Izmir and its seismic activity. The Tuzla fault has NE–SW trending lineaments and lies between the towns of Menderes and Cape Doganbey. This study intended to investigate crustal deformation and relative displacement along the Tuzla fault and Izmir Bay by two different geodetic techniques: GPS and precise leveling. Toward this aim, a geodetic network consisting of 16 points has been established. The first GPS observation campaign and precise leveling measurements were performed in 2009, and the second set of measurements was performed in 2010. The data collected by the GPS campaigns were processed with GAMIT/GLOBK software. The displacements inferred from GPS data are between 21mm/yr and 25mm/yr with respect to Eurasia as the fixed reference frame. In addition, the precise leveling results show that there is a vertical displacement in the region of around 7mm along the fault, which is higher than expected during a nine-month interval. [Copyright &y& Elsevier]

Turkish regional geoid models have been developed by employing a reference earth gravitational model, surface gravity observations and digital terrain models. The gravimetric geoid models provide a ready transformation from ellipsoidal heights to the orthometric heights through the use of GPS/leveling geoid heights determined through the national geodetic networks. The recent gravimetric models for Turkish territory were computed depending on OSU91 (TG-91) and EGM96 (TG-03) earth gravitational models. The release of the Earth Gravitational Model 2008 (EGM08), the collection of new surface gravity observations, the advanced satellite altimetry-derived gravity over the sea, and the availability of the high resolution digital terrain model have encouraged us to compute a new geoid model for Turkey. We used the Remove-Restore procedure based on EGM08 and applied Residual Terrain Model (RTM) reduction of the surface gravity data. Fast Fourier Transformation (FFT) was then used to obtain the residual quasigeoid from the reduced gravity. We restored the individual contributions of EGM08 and RTM to the whole quasi-geoid height (TQG-09). Since the Helmert orthometric height system is adopted in Turkey, the quasi-geoid model (TQG-09) was then converted to the geoid model (TG-09) by making use of Bouguer gravity anomalies and digital terrain model. After all we combined a gravimetric geoid model with GPS/leveling geoid heights in order to obtain a hybrid geoid model (THG-09) (or a transformation surface) to be used in GPS applications. The RMS of the post-fit residuals after the combination was found to be ± 0.95 cm, which represents the internal precision of the final combination. And finally, we tested the hybrid geoid model with GPS/leveling data, which were not used in the combination, to assess the external accuracy. Results show that the external accuracy of the THG-09 model is ± 8.4 cm, a precision previously not achieved in Turkey until this study. [ABSTRACT FROM AUTHOR]

Focuses on the application of a leap-frog trigonometric leveling with different sight distances on a sample test network at the Selcuk University Campus in Konya, Turkey in order to determine the optimum sight distances. Use of precise leveling to determine accurate heights; Overview of the principle of unidirectional trigonometric leveling; Means to get the total effect due to the deviation of the plumb line and the vertical refraction.

In a previous study, the author investigated the best suited static and kinematic models for deformation analysis. In that study, the best results were obtained with the Kalman-filtering technique for the kinematic model. In addition, the best kinematic surface model was determined. In this study, the conclusions of the previous work have been tested in the city of Aydın in the West Anatolia region of Turkey. Because the crustal movements are very slow, periodic observations have to be performed in the longterm. In addition, such observations have to be done with high precision. For this, precision leveling has been preferred for this study. Precision leveling data were already in place from the observations made each year from 1978 to 1985 in the West Anatolian city of Aydın. From this data, the vertical crustal movements have been determined using the best static and kinematic models determined by the author’s previous work. In conclusion, the average movements of geodetic control points have been determined as 1 cm per year. [ABSTRACT FROM AUTHOR]